There is much punditry about the effect of John Edwards on the 2008 Democratic Primary, and what would have happened had his affair been exposed earlier or he simply did the right thing and not ran in the first place.
Edwards effect on 2008
What many are missing is the changed dynamics that we will never know. There are pollsters citing "evidence" from a known reality, when we are pondering an unknown entity. For example, you can't say that it is clear that Michael Jordan would never have made it in baseball because the "evidence" shows he wasn't able to make it to the major leagues in the 1990's.
You would be missing decades of lost time that could have been used building and cultivating baseball skills that instead he used the time for basketball.
In this case, Edwards was one of the most aggressive challengers to Hillary Clinton, when the race shaped up as Hillary versus everyone else. In fact it was he who established the foundation for Obama in often angry tone that Obama felt that he couldn't do.
Subtract Edwards, and who would have made that case?
If Obama made it, he is he the angry black man?
If he doesn't make it does he have what it takes to win?
The fact is every day the race is changed, and in unpredictable ways.
It is my belief that Obama navigated a Perfect Storm.
He needed the media to help him through the Rev. Wright deal, they did.
He needed the other candidates to attack Hillary, they did.
He needed Hillary to make big mistakes and have the media amplify, she and they did.
He needed to convince people that he was ready to be POTUS, he did.
Yet, take away Edwards for all those months when he was viable, and Hillary could made an insider vs. rookie case much easier. Edwards brought an intensity as an outsider. Hillary brought an intensity as an insider. Obama brought the idea of change as an outsider.
Hillary would have had an extra opportunity to stop the Obama candidacy before it ever started.
I would guess it would have been about 15% more likely.
As it was, I think Obama had less than 10% odds to win the Democratic Primary.